diff --git a/docs/tutorial-2017.rst b/docs/tutorial-2017.rst deleted file mode 100644 index a0d5a61..0000000 --- a/docs/tutorial-2017.rst +++ /dev/null @@ -1,366 +0,0 @@ -.. _lister-tutorial-2017: - -Tutorial: list the content of your favorite forge in just a few steps -===================================================================== - -(the `original version -`_ -of this article appeared on the Software Heritage blog) - -Back in November 2016, Nicolas Dandrimont wrote about structural code changes -`leading to a massive (+15 million!) upswing in the number of repositories -archived by Software Heritage -`_ -through a combination of automatic linkage between the listing and loading -scheduler, new understanding of how to deal with extremely large repository -hosts like `GitHub `_, and activating a new set of -repositories that had previously been skipped over. - -In the post, Nicolas outlined the three major phases of work in Software -Heritage's preservation process (listing, scheduling updates, loading) and -highlighted that the ability to preserve the world's free software heritage -depends on our ability to find and list the repositories. - -At the time, Software Heritage was only able to list projects on -GitHub. Focusing early on GitHub, one of the largest and most active forge in -the world, allowed for a big value-to-effort ratio and a rapid launch for the -archive. As the old Italian proverb goes, "Il meglio è nemico del bene," or in -modern English parlance, "Perfect is the enemy of good," right? Right. So the -plan from the beginning was to implement a lister for GitHub, then maybe -implement another one, and then take a few giant steps backward and squint our -eyes. - -Why? Because source code hosting services don't behave according to a unified -standard. Each new service requires dedicated development time to implement a -new scraping client for the non-transferable requirements and intricacies of -that service's API. At the time, doing it in an extensible and adaptable way -required a level of exposure to the myriad differences between these services -that we just didn't think we had yet. - -Nicolas' post closed by saying "We haven't carved out a stable API yet that -allows you to just fill in the blanks, as we only have the GitHub lister -currently, and a proven API will emerge organically only once we have some -diversity." - -That has since changed. As of March 6, 2017, the Software Heritage **lister -code has been aggressively restructured, abstracted, and commented** to make -creating new listers significantly easier. There may yet be a few kinks to iron -out, but **now making a new lister is practically like filling in the blanks**. - -Fundamentally, a basic lister must follow these steps: - -1. Issue a network request for a service endpoint. -2. Convert the response into a canonical format. -3. Populate a work queue for fetching and ingesting source repositories. - -Steps 1 and 3 are generic problems, so they can get generic solutions hidden -away in the base code, most of which never needs to change. That leaves us to -implement step 2, which can be trivially done now for services with a clean web -APIs. - -In the new code, we've tried to hide away as much generic functionality as -possible, turning it into set-and-forget plumbing between a few simple -customized elements. Different hosting services might use different network -protocols, rate-limit messages, or pagination schemes, but, as long as there is -some way to get a list of the hosted repositories, we think that the new base -code will make getting those repositories much easier. - -First, let me give you the 30,000 foot view… - -The old GitHub-specific lister code looked like this (265 lines of Python): - -.. figure:: images/old_github_lister.png - -By contrast, the new GitHub-specific code looks like this (34 lines of Python): - -.. figure:: images/new_github_lister.png - -And the new BitBucket-specific code is even shorter and looks like this (24 lines of Python): - -.. figure:: images/new_bitbucket_lister.png - -And now this is common shared code in a few abstract base classes, with some new -features and loads of docstring comments (in red): - -.. figure:: images/new_base.png - -So how does the lister code work now, and **how might a contributing developer -go about making a new one** - -The first thing to know is that we now have a generic lister base class and ORM -model. A subclass of the lister base should already be able to do almost -everything needed to complete a listing task for a single service -request/response cycle with the following implementation requirements: - -1. A member variable must be declared called ``MODEL``, which is equal to a - subclass (Note: type, not instance) of the base ORM model. The reasons for - using a subclass is mostly just because different services use different - incompatible primary identifiers for their repositories. The model - subclasses are typically only one or two additional variable declarations. - -2. A method called ``transport_request`` must be implemented, which takes the - complete target identifier (e.g., a URL) and tries to request it one time - using whatever transport protocol is required for interacting with the - service. It should not attempt to retry on timeouts or do anything else with - the response (that is already done for you). It should just either return - the response or raise a ``FetchError`` exception. - -3. A method called ``transport_response_to_string`` must be implemented, which - takes the entire response of the request in (1) and converts it to a string - for logging purposes. - -4. A method called ``transport_quota_check`` must be implemented, which takes - the entire response of the request in (1) and checks to see if the process - has run afoul of any query quotas or rate limits. If the service says to - wait before making more requests, the method should return ``True`` and also - the number of seconds to wait, otherwise it returns ``False``. - -5. A method called ``transport_response_simplified`` must be implemented, which - also takes the entire response of the request in (1) and converts it to a - Python list of dicts (one dict for each repository) with keys given - according to the aforementioned ``MODEL`` class members. - -Because 1, 2, 3, and 4 are basically dependent only on the chosen network -protocol, we also have an HTTP mix-in module, which supplements the lister base -and provides default implementations for those methods along with optional -request header injection using the Python Requests library. The -``transport_quota_check`` method as provided follows the IETF standard for -communicating rate limits with `HTTP code 429 -`_ which some hosting services -have chosen not to follow, so it's possible that a specific lister will need to -override it. - -On top of all of that, we also provide another layer over the base lister class -which adds support for sequentially looping over indices. What are indices? -Well, some services (`BitBucket `_ and GitHub for -example) don't send you the entire list of all of their repositories at once, -because that server response would be unwieldy. Instead they paginate their -results, and they also allow you to query their APIs like this: -``https://server_address.tld/query_type?start_listing_from_id=foo``. Changing -the value of 'foo' lets you fetch a set of repositories starting from there. We -call 'foo' an index, and we call a service that works this way an indexing -service. GitHub uses the repository unique identifier and BitBucket uses the -repository creation time, but a service can really use anything as long as the -values monotonically increase with new repositories. A good indexing service -also includes the URL of the next page with a later 'foo' in its responses. For -these indexing services we provide another intermediate lister called the -indexing lister. Instead of inheriting from :class:`ListerBase -`, the lister class would inherit -from :class:`IndexingLister -`. Along with the -requirements of the lister base, the indexing lister base adds one extra -requirement: - -1. A method called ``get_next_target_from_response`` must be defined, which - takes a complete request response and returns the index ('foo' above) of the - next page. - -So those are all the basic requirements. There are, of course, a few other -little bits and pieces (covered for now in the code's docstring comments), but -for the most part that's it. It sounds like a lot of information to absorb and -implement, but remember that most of the implementation requirements mentioned -above are already provided for 99% of services by the HTTP mix-in module. It -looks much simpler when we look at the actual implementations of the two -new-style indexing listers we currently have… - -When developing a new lister, it's important to test. For this, add the tests -(check `swh/lister/*/tests/`) and register the celery tasks in the main -conftest.py (`swh/lister/core/tests/conftest.py`). - -Another important step is to actually run it within the -docker-dev (:ref:`run-lister-tutorial`). - -This is the entire source code for the BitBucket repository lister:: - - # Copyright (C) 2017 the Software Heritage developers - # License: GNU General Public License version 3 or later - # See top-level LICENSE file for more information - - from urllib import parse - from swh.lister.bitbucket.models import BitBucketModel - from swh.lister.core.indexing_lister import IndexingHttpLister - - class BitBucketLister(IndexingHttpLister): - PATH_TEMPLATE = '/repositories?after=%s' - MODEL = BitBucketModel - - def get_model_from_repo(self, repo): - return {'uid': repo['uuid'], - 'indexable': repo['created_on'], - 'name': repo['name'], - 'full_name': repo['full_name'], - 'html_url': repo['links']['html']['href'], - 'origin_url': repo['links']['clone'][0]['href'], - 'origin_type': repo['scm'], - 'description': repo['description']} - - def get_next_target_from_response(self, response): - body = response.json() - if 'next' in body: - return parse.unquote(body['next'].split('after=')[1]) - else: - return None - - def transport_response_simplified(self, response): - repos = response.json()['values'] - return [self.get_model_from_repo(repo) for repo in repos] - -And this is the entire source code for the GitHub repository lister:: - - # Copyright (C) 2017 the Software Heritage developers - # License: GNU General Public License version 3 or later - # See top-level LICENSE file for more information - - import time - from swh.lister.core.indexing_lister import IndexingHttpLister - from swh.lister.github.models import GitHubModel - - class GitHubLister(IndexingHttpLister): - PATH_TEMPLATE = '/repositories?since=%d' - MODEL = GitHubModel - - def get_model_from_repo(self, repo): - return {'uid': repo['id'], - 'indexable': repo['id'], - 'name': repo['name'], - 'full_name': repo['full_name'], - 'html_url': repo['html_url'], - 'origin_url': repo['html_url'], - 'origin_type': 'git', - 'description': repo['description']} - - def get_next_target_from_response(self, response): - if 'next' in response.links: - next_url = response.links['next']['url'] - return int(next_url.split('since=')[1]) - else: - return None - - def transport_response_simplified(self, response): - repos = response.json() - return [self.get_model_from_repo(repo) for repo in repos] - - def request_headers(self): - return {'Accept': 'application/vnd.github.v3+json'} - - def transport_quota_check(self, response): - remain = int(response.headers['X-RateLimit-Remaining']) - if response.status_code == 403 and remain == 0: - reset_at = int(response.headers['X-RateLimit-Reset']) - delay = min(reset_at - time.time(), 3600) - return True, delay - else: - return False, 0 - -We can see that there are some common elements: - -* Both use the HTTP transport mixin (:class:`IndexingHttpLister - `) just combines - :class:`ListerHttpTransport - ` and - :class:`IndexingLister - `) to get most of the - network request functionality for free. - -* Both also define ``MODEL`` and ``PATH_TEMPLATE`` variables. It should be - clear to developers that ``PATH_TEMPLATE``, when combined with the base - service URL (e.g., ``https://some_service.com``) and passed a value (the - 'foo' index described earlier) results in a complete identifier for making - API requests to these services. It is required by our HTTP module. - -* Both services respond using JSON, so both implementations of - ``transport_response_simplified`` are similar and quite short. - -We can also see that there are a few differences: - -* GitHub sends the next URL as part of the response header, while BitBucket - sends it in the response body. - -* GitHub differentiates API versions with a request header (our HTTP - transport mix-in will automatically use any headers provided by an - optional request_headers method that we implement here), while - BitBucket has it as part of their base service URL. BitBucket uses - the IETF standard HTTP 429 response code for their rate limit - notifications (the HTTP transport mix-in automatically handles - that), while GitHub uses their own custom response headers that need - special treatment. - -* But look at them! 58 lines of Python code, combined, to absorb all - repositories from two of the largest and most influential source code hosting - services. - -Ok, so what is going on behind the scenes? - -To trace the operation of the code, let's start with a sample instantiation and -progress from there to see which methods get called when. What follows will be -a series of extremely reductionist pseudocode methods. This is not what the -code actually looks like (it's not even real code), but it does have the same -basic flow. Bear with me while I try to lay out lister operation in a -quasi-linear way…:: - - # main task - - ghl = GitHubLister(lister_name='github.com', - api_baseurl='https://github.com') - ghl.run() - -⇓ (IndexingLister.run):: - - # IndexingLister.run - - identifier = None - do - response, repos = ListerBase.ingest_data(identifier) - identifier = GitHubLister.get_next_target_from_response(response) - while(identifier) - -⇓ (ListerBase.ingest_data):: - - # ListerBase.ingest_data - - response = ListerBase.safely_issue_request(identifier) - repos = GitHubLister.transport_response_simplified(response) - injected = ListerBase.inject_repo_data_into_db(repos) - return response, injected - -⇓ (ListerBase.safely_issue_request):: - - # ListerBase.safely_issue_request - - repeat: - resp = ListerHttpTransport.transport_request(identifier) - retry, delay = ListerHttpTransport.transport_quota_check(resp) - if retry: - sleep(delay) - until((not retry) or too_many_retries) - return resp - -⇓ (ListerHttpTransport.transport_request):: - - # ListerHttpTransport.transport_request - - path = ListerBase.api_baseurl - + ListerHttpTransport.PATH_TEMPLATE % identifier - headers = ListerHttpTransport.request_headers() - return http.get(path, headers) - -(Oh look, there's our ``PATH_TEMPLATE``) - -⇓ (ListerHttpTransport.request_headers):: - - # ListerHttpTransport.request_headers - - override → GitHubLister.request_headers - -↑↑ (ListerBase.safely_issue_request) - -⇓ (ListerHttpTransport.transport_quota_check):: - - # ListerHttpTransport.transport_quota_check - - override → GitHubLister.transport_quota_check - -And then we're done. From start to finish, I hope this helps you understand how -the few customized pieces fit into the new shared plumbing. - -Now you can go and write up a lister for a code hosting site we don't have yet! diff --git a/docs/tutorial.rst b/docs/tutorial.rst index 8293015..e254bcd 100644 --- a/docs/tutorial.rst +++ b/docs/tutorial.rst @@ -1,365 +1,363 @@ .. _lister-tutorial: Tutorial: list the content of your favorite forge in just a few steps ===================================================================== Overview -------- The three major phases of work in Software Heritage's preservation process, on the technical side, are *listing software sources*, *scheduling updates* and *loading the software artifacts into the archive*. A previous effort in 2017 consisted in designing the framework to make lister a straightforward "fill in the blanks" process, based on gained experience on the diversity found in the listed services. This is the second iteration on the lister framework design, comprising a library and an API which is easier to work with and less "magic" (read implicit). This new design is part of a larger effort in redesigning the scheduling system for the recurring tasks updating the content of the archive. .. _fundamentals: Fundamentals ------------ Fundamentally, a basic lister must follow these steps: 1. Issue a network request for a service endpoint. 2. Convert the response data into a model object. 3. Send the model object to the scheduler. Steps 1 and 3 are generic problems, that are often already solved by helpers or in other listers. That leaves us mainly to implement step 2, which is simple when the remote service provides an API. .. _prerequisites: Prerequisites ------------- Skills: * object-oriented Python * requesting remote services through HTTP * scrapping if no API is offered Analysis of the target service. Prepare the following elements to write the lister: * instance names and URLs * requesting scheme: base URL, path, query_string, POST data, headers * authentication types and which one to support, if any * rate-limiting: HTTP codes and headers used * data format: JSON/XML/HTML/...? * mapping between remote data and needed data (ListedOrigin model, internal state) We will now walk through the steps to build a new lister. Please use this template to start with: :download:`new_lister_template.py` .. _lister-declaration: Lister declaration ------------------ In order to write a lister, two basic elements are required. These are the :py:class:`Lister` base class and the :py:class:`ListedOrigin` scheduler model class. Optionally, for listers that need to keep a state and support incremental listing, an additional object :py:class:`ListerState` will come into play. Each lister must subclass :py:class:`Lister ` either directly or through a subclass such as :py:class:`StatelessLister ` for stateless ones. We extensively type-annotate our listers, as any new code, which makes proeminent that those lister classes are generic, and take the following parameters: * :py:class:`Lister`: the lister state type, the page type * :py:class:`StatelessLister`: only the page type You can can start by declaring a stateless lister and leave the implementation of state for later if the listing needs it. We will see how to in :ref:`handling-lister-state`. Both the lister state type and the page type are user-defined types. However, while the page type may only exist as a type annotation, the state type for a stateful lister must be associated with a concrete object. The state type is commonly defined as a dataclass whereas the page type is often a mere annotation, potentially given a nice alias. Example lister declaration:: NewForgePage = List[Dict[str, Any]] @dataclass class NewForgeListerState: ... class NewForgeLister(Lister[NewForgeListerState, NewForgePage]): LISTER_NAME = "My" ... The new lister must declare a name through the :py:attr:`LISTER_NAME` class attribute. .. _lister-construction: Lister construction ------------------- The lister constructor is only required to ask for a :py:class:`SchedulerInterface` object to pass to the base class. But it does not mean that it is all that's needed for it to useful. A lister need information on which remote service to talk to. It needs an URL. Some services are centralized and offered by a single organization. Think of Github. Others are offered by many people across the Internet, each using a different hosting, each providing specific data. Think of the many Gitlab instances. We need a name to identify each instance, and even if there is only one, we need its URL to access it concretely. Now, you may think of any strategy to infer the information or hardcode it, but the base class needs an URL and an instance name. In any case, for a multi-instance service, you better be explicit and require the URL as constructor argument. We recommend the URL to be some form of a base URL, to be concatenated with any variable part appearing either because there exist multiple instances or the URL need recomputation in the listing process. If we need any credentials to access a remote service, and do so in our polite but persistent fashion (remember that we want fresh information), you are encouraged to provide support for authenticated access. The base class support handling credentials as a set of identifier/secret pair. It knows how to load from a secrets store the right ones for the current ("lister name", "instance name") setting, if none were originally provided through the task parameters. You can ask for other types of access tokens in a separate parameter, but then you lose this advantage. Example of a typical lister constructor:: def __init__( self, scheduler: SchedulerInterface, url: str, instance: str, credentials: CredentialsType = None, ): super().__init__( scheduler=scheduler, url=url, instance=instance, credentials=credentials, ) ... .. _core-lister-functionality: Core lister functionality ------------------------- For the lister to contribute data to the archive, you now have to write the logic to fetch data from the remote service, and format it in the canonical form the scheduler expects, as outined in :ref:`fundamentals`. To this purpose, the two methods to implement are:: def get_pages(self) -> Iterator[NewForgePage]: ... def get_origins_from_page(self, page: NewForgePage) -> Iterator[ListedOrigin]: ... Those two core functions are called by the principal lister method, :py:meth:`Lister.run`, found in the base class. :py:meth:`get_pages` is the guts of the lister. It takes no arguments and must produce data pages. An iterator is fine here, as the :py:meth:`Lister.run` method only mean to iterate in a single pass on it. This method gets its input from a network request to a remote service's endpoint to retrieve the data we long for. Depending on whether the data is adequately structured for our purpose can be tricky. Here you may have to show off your data scraping skills, or just consume a well-designed API. Those aspects are discussed more specifically in the section :ref:`handling-specific-topics`. In any case, we want the data we return to be usefully filtered and structured. The easiest way to create an iterator is to use the `yield` keyword. Yield each data page you have structured in accordance with the page type you have declared. The page type exists only for static type checking of data passed from :py:meth:`get_pages` to :py:meth:`get_origins_from_page`; you can choose whatever fits the bill. :py:meth:`get_origins_from_page` is simpler. For each individual software origin you have received in the page, you convert and yield a :py:class:`ListedOrigin` model object. This datatype has the following mandatory fields: * lister id: you generally fill this with the value of :py:attr:`self.lister_obj.id` * visit type: the type of software distribution format the service provides. For use by a corresponding loader. It is an identifier, so you have to either use an existing value or craft a new one if you get off the beaten track and tackle a new software source. But then you will have to discuss the name with the core developers. Example: Phabricator is a forge that can handle Git or SVN repositories. The visit type would be "git" when listing such a repo that provides a Git URL that we can load. * origin URL: an URL that, combined with the visit type, will serve as the input of loader. This datatype can also further be detailed with the optional fields: * last update date: freshness information on this origin, which is useful to the scheduler for optimizing its scheduling decisions. Fill it if provided by the service, at no substantial additional runtime cost, e.g. in the same request. * extra loader arguments: extra parameters to be passed to the loader for it to be able to load the origin. It is needed for example when additional context is needed along with the URL to effectively load from the origin. See the definition of ListedOrigin_. Now that that we showed how those two methods operate, let's put it together by showing how they fit in the principal :py:meth:`Lister.run` method:: def run(self) -> ListerStats: full_stats = ListerStats() try: for page in self.get_pages(): full_stats.pages += 1 origins = self.get_origins_from_page(page) full_stats.origins += self.send_origins(origins) self.commit_page(page) finally: self.finalize() if self.updated: self.set_state_in_scheduler() return full_stats :py:meth:`Lister.send_origins` is the method that sends listed origins to the scheduler. The :py:class:`ListerState` datastructure, defined along the base lister class, is used to compute the number of listed pages and origins in a single lister run. It is useful both for the scheduler that automatically collects this information and to test the lister. You see that the bulk of a lister run consists in streaming data gathered from the remote service to the scheduler. And this is done under a ``try...finally`` construct to have the lister state reliably recorded in case of unhandled error. We will explain the role of the remaining methods and attributes appearing here in the next section as it is related to the lister state. .. _ListedOrigin: https://archive.softwareheritage.org/browse/swh:1:rev:03460207a17d82635ef5a6f12358392143eb9eef/?origin_url=https://forge.softwareheritage.org/source/swh-scheduler.git&path=swh/scheduler/model.py&revision=03460207a17d82635ef5a6f12358392143eb9eef#L134-L177 .. _handling-lister-state: Handling lister state --------------------- With what we have covered until now you can write a stateless lister. Unfortunately, some services provide too much data to efficiently deal with it in a one-shot fashion. Listing a given software source can take several hours or days to process. Our listers can also give valid output, but fail on an unexpected condition and would have to start over. As we want to be able to resume the listing process from a given element, provided by the remote service and guaranteed to be ordered, such as a date or a numeric identifier, we need to deal with state. The remaining part of the lister API is reserved for dealing with lister state. If the service to list has no pagination, then the data set to handle is small enough to not require keeping lister state. In the opposite case, you will have to determine which piece of information should be recorded in the lister state. As said earlier, we recommend declaring a dataclass for the lister state:: @dataclass class NewForgeListerState: current: str = "" class NewForgeLister(Lister[NewForgeListerState, NewForgePage]): ... A pair of methods, :py:meth:`state_from_dict` and :py:meth:`state_to_dict` are used to respectively import lister state from the scheduler and export lister state to the scheduler. Some fields may need help to be serialized to the scheduler, such as dates, so this needs to be handled there. Where is the state used? Taking the general case of a paginating service, the lister state is used at the beginning of the :py:meth:`get_pages` method to initialize the variables associated with the last listing progress. That way we can start from an arbitrary element, or just the first one if there is no last lister state. The :py:meth:`commit_page` is called on successful page processing, after the new origins are sent to the scheduler. Here you should mainly update the lister state by taking into account the new page processed, e.g. advance a date or serial field. Finally, upon either completion or error, the :py:meth:`finalize` is called. There you must set attribute :py:attr:`updated` to True if you were successful in advancing in the listing process. To do this you will commonly retrieve the latest saved lister state from the scheduler and compare with your current lister state. If lister state was updated, ultimately the current lister state will be recorded in the scheduler. We have now seen the stateful lister API. Note that some listers may implement more flexibility in the use of lister state. Some allow an `incremental` parameter that governs whether or not we will do a stateful listing or not. It is up to you to support additional functionality if it seems relevant. .. _handling-specific-topics: Handling specific topics ------------------------ Here is a quick coverage of common topics left out from lister construction and :py:meth:`get_pages` descriptions. Sessions ^^^^^^^^ When requesting a web service repeatedly, most parameters including headers do not change and could be set up once initially. We recommend setting up a e.g. HTTP session, as instance attribute so that further requesting code can focus on what really changes. Some ubiquitous HTTP headers include "Accept" to set to the service response format and "User-Agent" for which we provide a recommended value :py:const:`USER_AGENT` to be imported from :py:mod:`swh.lister`. Authentication is also commonly provided through headers, so you can also set it up in the session. Transport error handling ^^^^^^^^^^^^^^^^^^^^^^^^ We generally recommend logging every unhandleable error with the response content and then immediately stop the listing by doing an equivalent of :py:meth:`Response.raise_for_status` from the `requests` library. As for rate-limiting errors, we have a strategy of using a flexible decorator to handle the retrying for us. It is based on the `tenacity` library and accessible as :py:func:`throttling_retry` from :py:mod:`swh.lister.utils`. Pagination ^^^^^^^^^^ This one is a moving target. You have to understand how the pagination mechanics of the particular service works. Some guidelines though. The identifier may be minimal (an id to pass as query parameter), compound (a set of such parameters) or complete (a whole URL). If the service provides the next URL, use it. The piece of information may be found either in the response body, or in a header. Once identified, you still have to implement the logic of requesting and extracting it in a loop and quitting the loop when there is no more data to fetch. Page results ^^^^^^^^^^^^ First, when retrieving page results, which involves some protocols and parsing logic, please make sure that any deviance from what was expected will result in an informational error. You also have to simplify the results, both with filtering request parameters if the service supports it, and by extracting from the response only the information needed into a structured page. This all makes for easier debugging. Testing your lister ------------------- When developing a new lister, it's important to test. For this, add the tests (check `swh/lister/*/tests/`) and register the celery tasks in the main conftest.py (`swh/lister/core/tests/conftest.py`). Another important step is to actually run it within the docker-dev (:ref:`run-lister-tutorial`). More about listers ------------------ See current implemented listers as examples (GitHub_, Bitbucket_, CGit_, GitLab_ ). -Old (2017) lister tutorial :ref:`lister-tutorial-2017` - .. _GitHub: https://forge.softwareheritage.org/source/swh-lister/browse/master/swh/lister/github/lister.py .. _Bitbucket: https://forge.softwareheritage.org/source/swh-lister/browse/master/swh/lister/bitbucket/lister.py .. _CGit: https://forge.softwareheritage.org/source/swh-lister/browse/master/swh/lister/cgit/lister.py .. _GitLab: https://forge.softwareheritage.org/source/swh-lister/browse/master/swh/lister/gitlab/lister.py